Quartz working



E. R. BERRY QUARTZ WORKING April 20 1926.

Filed March 29, 1921 H fnventozfzi Edward R. Be gf His wuohnel EDWARD R. BERRY, OI MALDEN,

'terial,

Patented -Apr 20, 1926.

UNITED sTAra-s I 1,581,829 PATENT oFFrca.

COMPANY, A

MASSACHUSETTS, ASSIGNOR' T0 GEIN'ERAL CORPORATION Oil? NEW YORK.

QUARTZ WORKING.

Application filed March 29, 1921. Serial No. 456,577.

To all whom it may concern:

Be it known that I, EDWARDR. BERRY, a citizen of the United States, residing at Malden, in the county of Middlesex, State of Massachusetts, have invented certain new and useful Improvements in Quartz Working, of which the following is a specification.

-The present invention relates to the proluction of substantially bubble-free silica glass or vitreous quartz.

One of the difficulties encountered in the working of silica is the cracking of quartz crystal during heating, and the consequent presence of air'bubb es in the fused mathese bubbles frequently being so numerous and so small as to give the silica a milky or cloudy appearance.

In accordance with my invention, substantially bubble-free silica is produced by extruding silica while plastic through a contracted opening, preferably a narrow elongated slit. As a result of the molten silica being spread out into a thin ribbon, the entrapped air bubbles are substantially entirely eliminated. The extruded silica then is caused to coalesce in a vacuum forming clear homogeneous slugs.

The accompanying drawing illustrates in Fig. 1 in vertical section an apparatus suitable for carrying out my invention; Figs. 2 and 3, respectively, are detail views of the extrusion duct being respectively vertical and horizontal sections.

cover by the conductors 5, 6.

lar and serve also to convey a The furnace shown in Fig. 1 is particularly adapted to carry out. a fusion at reduced gaseous pressure. I wish it to be understood,'however, that the benefits of my invention are not entirely dependent upon the practice of the process in a vacuum although benefits are derived by the use of a vacuum.

Referring to Fig. '1 of the drawing, the furnace here shown comprises a tankl having a cover 2 bolted thereto with a gastight joint. The cover maybe provided with an extension 3 indicated in part broken away. A heater 4 consisting of graphite or other suitable material is suspended from the These conductors are suitably insulated from each other and from the cover as indicated and are connected to external terminals (not shown). Preferably they are made tubucooling fluid to the terminal clamps 7 ,8. A heat screen tl preferably surrounds the heater. Located 1n the heating space within the heater 4' is nnncrn rc a container, 10 which has two compartments j i separated by a transverse wall 11 containing a a duct 12, as bestshown in Figs. 2 and 3. The duct 12may have various shapes but preferabl narrow s it, as indicated. For example, the duct 11 may be 5 in length and in width. The container .10 is supported by a pedestal 13 resting on the terminal cap 14 of the heater 4. The container consists of material inert with respect to molten silica, as for example graphite.

In accordance with my invention a quantity of pure silica, as for example quartz crystal, is placed in the upper compartment of the receptacle 10, and the interior of the it is constituted of an elongated furnace is exhausted of air through the tube 16. A heating current is conveyed to the resistor 4 to bring the silica to a plastic state. When quartz crystal is used, it cracks into many pieces at about 550 C., but subsequent coalescence of these pieces will trap little gas in so far as the gases within the container have been removed. As it is not possible to entirely remove the gas some bubles will be trapped in the mass when the pieces of quartz' coalesce as a glassy mass at about 1650 C. To bring the silica glass to thin liquidity would require a temperature of about 2000 C(with large accompanying losses of silica by vaporization. Instead of attempting to remove gas bubbles by heating the silica glass to sufficient liquidity. to cause the gas bubbles to, rise, I prefer to heat the silica to a. plastic state only, say, up

to 1750 C. and cause the plastic mass to stem 18 passes through a suitable bushing in the, cover extension 3. The-material issuing from the constricted opening'is substantial ly free from bubbles. the elimination of bubbles is due to the high surface tension of the. plastic silica which It is probable that by virtue of the large surface exposed and the proximity of the gas cavities to the surface cause the walls of the cavities or bubbles to collapse.

The material may utilized in the form of slugs in subsequent operations, or the silica may be used directly in ribbon form. I

What I claim as new and desire to secure by Letters Patent of the United States, is

1. The method of freeing silica from gas bubbles which consists in extruding the silica in a plastic state in a vacuum.through an o ening sufliciently restricted to cause bubb es to 'break through the surface of the silica, and thereupon causing said extruded silica to coalesce in a vacuum.

2. Thewmethod of freeing silica from entrapped cavities which consists in extruding the silica in a plastic state through a slit of such narrowness that the surface tension of the silica causes the cavities to collapse.

3. The method of producing clear vitreous quartz which consists in melting crystalline quartz in an attenuated atmosphere, removing bubbles therefrom by passing the quartz while heated to a temperature of about 17 50 0. through a restrictedopening, and causing the extruded silica to recoalesce.

4. An apparatus for freeing silica from be collected in the lower chamber, caused to coalesce as indicated, and I I sht 1nto the other conta1ner,'and means for maintaining a vacuum about said container.

. mamas entrapped air which consists of the combination 'of two'containe'rs communicating with each other by a narrow slit, heating means for causin quartz in one c0ntaine1 to become sufiiciently plastic to pass through said 5. The process of producing vitreous silica substantially free from bubbles which concrystalline quartz in a 'vacu- I sists in fusin um," forcing t e fusion while plastic through a restricted duct in a vacuum, and causing the extruded silica to coalesce in the form of s ugs.

6. The step in the process of, making clear silica ware which consists in forcing under pressure plastic silica containing entrapped ubblcs throu h a duct of such small dimensions that the ubbles in said silica are largely eliminated. 7. The step in the process of making clear silica w'are which consists in spreading plastic silica containing gas bubbles into thin ribbons thereby eliminating a substantial number of said bubbles and thereupon causing said ribbon to coalesce in a vacuum.

In witness whereof, I have hereunto set- 

